1. Technical Field
The present invention relates to a method of preparing a toner using micro-suspension particles, and a toner prepared using the method, and more particularly, to a toner using micro-suspension particles which can save manufacturing costs and enhance charging ability and cleaning properties, and a toner prepared using the method.
2. Background Art
There is increasing demand for a toner optimized for high speed printing, particularly a toner using a polyester resin.
The method of preparing such a toner can be categorized into physical and chemical methods.
The physical methods include pulverization. Pulverization is a method of preparing a toner by melt-mixing a colorant, charge control agent and the like with a resin such as polyester, dispersing the resulting melt-mixture homogenously and then pulverizing and classifying the toner composition obtained. The pulverization method requires a pulverizing device in order to pulverize the toner composition. Therefore, it is expensive to prepare a toner with small particle diameters, and also inefficient. Moreover, when pulverizing the toner composition, particles with a wide particle size distribution are likely to be formed, and in order to obtain an image of high resolution and/or high gradation, it is necessary to classify and remove fine particles with a diameter of 3 μm or less and coarse particles with a diameter of 20 μm or greater. In addition, if the additives are not dispersed homogenously in the toner, fluidity, developability, durability, and/or image quality of the toner may be degraded.
Meanwhile, chemical methods include suspension-polymerization method and emulsion-aggregation method.
Suspension-polymerization is a method of preparing a toner by suspension-polymerizing the toner materials in a suspension medium. Canon etc. possesses such type of technology (U.S. Pat. No. 6,177,223). This method may improve the problems regarding the pulverization method, but is disadvantageous in that only styrene-acrylic copolymers are used as basic resin, and the toner particles obtained thereby are sphere-shaped, having a reduced cleaning property. Therefore, toner prepared by the suspension-polymerization method causes the toner to remain on a photoconductor of an electrophotographic image forming device. The toner remained and accumulated on the photoconductor may produce poor image quality, and may result in contamination of a charging roller and the like, as well as a problem of not being able to achieve the original charge ability.
Another chemical method of preparing a toner composition is emulsion-aggregation (U.S. Pat. Nos. 5,916,725, 6,268,103). This method includes preparing a micro-emulsion resin particle composition through an emulsion polymerization reaction, and aggregating the composition with a separate dispersion such as pigment dispersion. Such a method may improve the problems regarding the pulverization method and results in the toner particles being formed to be non-spherical by controlling aggregating conditions. However, the method is disadvantageous in that only styrene-acrylic copolymers are used as basic resin, and preparation of dispersion such as pigment dispersion should be further included.
The two chemical methods of preparing toner described above use only styrene-acrylic copolymers as basic resin. Therefore, polyester resin having excellent properties such as excellent fluidity, excellent dispersion of pigments derived from the chemical structure of the resin and excellent transparency, cannot be used in general color toners and toners for high speed-printing.
A method of preparing a toner using a polyester resin includes a method of using self-water dispersible polyester (U.S. Pat. No. 5,916,725), but this method requires resin having sodium sulfonate group or the like in its chain in order to make self-water dispersion possible. Also, the toner, which includes many functional groups introduced in this way is likely to be influenced by external environmental factors such as moisture after manufacturing, which may decrease the stability of the toner.
U.S. Pat. No. 6,416,917 discloses a dry toner including a toner binder and a colorant. The toner binder includes a high molecular weight polyester resin and a low molecular weight oligomeric resin having urea or urethane bonds. Such a toner accompanies a chemical reaction during preparation of the toner particles, making it difficult to control the properties of the toner, and condensation cannot be easily achieved within the aqueous phase.
Japanese Patent No. 3063269 discloses a method of preparing a toner by dissolving a resin having acidic groups in an organic solvent, disperse-mixing a colorant in the solution, and then neutralizing the acid groups with a base through phase transition emulsification. However, when preparing a toner using this method, it is difficult to increase the solid contents, and viscosity increases at the point of phase-transition, raising the shear rate. Moreover, controlling the morphology is difficult, and thus a spherical toner is likely to be formed. Also, a separate classifying process may be required due to a difficulty in obtaining a narrow size distribution. Moreover, water-oil-water (W/O/W) particles may be formed during the phase-transition emulsification process, having possibility to form pores within the toner particles. In addition, a high-speed shearing machine or the like must be used in order to disperse the colorant in the organic solvent in which the resin is dissolved.